1. Field of the Invention
The present invention relates generally to the field of a communication apparatus, a communication method, a communication program and an information recording medium having the communication program recorded thereon, and more particularly to the communication apparatus and method for performing at least one of transmission and reception of data relative to the other processing apparatus connected to a network, the communication program for executing such communication and the information recording medium on which the communication program has been recorded.
2. Related Art
Recently, a so-called “IEEE1394 Standard” (officially known as “IEEEStd. 1394-1995 IEEE Standard for a High Performance Serial Bus” and “IEEEStd. 1394a-2000 IEEE Standard for a High Performance Serial Bus-Amendment 1”) has been widely utilized as a standard such as a serial on the basis of which a real-time transmission of information can be made through a network between processing apparatuses (e.g. a personal computer and a digital video camera). Many products such as personal computers and digital video cameras provided with a serial port based on the above-mentioned standard have become commercially practical.
The IEEE1394 standard enables data to be transmitted at a high transmission speed, with the result that a high degree of freedom in formation of topology can be ensured, and the standard is suitable for transmission of real-time data through an isochronous data transmission, thus providing advantages effects, as well as high usability in comparison with the conventional interface standards. Data transmission based on the IEEE1394 requires a physical establishment of connection for data transmission between respective information processing apparatuses (hereinafter referred merely to as the “apparatus”).
In some of the apparatuses, which are interconnected through the serial interface based on the above-mentioned IEEE1304 standard, the interconnection between the apparatuses is managed based on a standard called “IEC-61883 Part 1 standard”, in addition to the above-mentioned IEEE1394 standard.
According to the IEC-61883 Part 1 standard, when a certain apparatus based on this standard is connected to the other apparatus to carry out data transmission, logic plugs (i.e., terminals) for transmission of the data are defined on the respective apparatus, and further, information indicative of the connection state of the respective plugs (more specifically, a register memory that stores in real time establishment of connection of apparatuses, which are connected through the above-mentioned plugs (hereinafter referred as the “plug register”)) is defined for each of the plugs, and a control is made to update the stored contents in the plug register in accordance with variation of connection state through the plugs, to manage the respective connection states, as described in Japanese Laid-Open Patent Application No. 2002-217907, pages 3 and 4.
The IEEE1394 standard is established for a wider range of apparatus in comparison with the IEC-61883 Part 1 standard. Accordingly, there is a possibility that there exists an apparatus, which is not based on the IEC-61883 Part 1 standard, but is based on the IEEE1394 standard. There is also a possibility that there exists an apparatus, which is not based per se on the IEC-61883 Part 1 standard, but enables transmission and reception of data based on the IEEE1394 standard through the above-mentioned serial bus.
The establishment of connection for isochronous data transmission between the respective apparatuses based on the IEC-61883 Part 1 standard, and release thereof are controlled through the updated contents stored n the above-mentioned plug resister in this manner.
The update of the stored contents is carried out at the timing of a lock-transaction defined in the above-mentioned IEC-61883 Part 1 standard. When the update of the stored contents provides a state in which the connection is established, the isochronous data are transmitted through the serial bus, and disconnection of the connection causes the transmission of the isochronous data to be halted.
The connections based on the IEC-61883 Part 1 standard include two kinds of connection, i.e., a so-called “Broadcast connection” and a so-called “Point-to point connection” (hereinafter referred to as the “p2p connection”).
Of these connections, the Broadcast connection is composed of two kinds of connection, i.e., Broadcast-out connection in which a single plug (i.e., an output plug) provided in a transmitting apparatus is connected to only an isochronous channel on the serious bus, irrespective of the plug of the receiving apparatus, and Broadcast-in connection in which a single plug (i.e., an input plug) provided in a receiving apparatus is connected to only a single isochronous channel on the serious bus, irrespective of the plug of the transmitting apparatus.
On the other hand, the p2p connection is connection in which a plug provided in a single apparatus (i.e., the plug having a function of input or output in the single apparatus) is connected to a plug provided in the other apparatus, in which connection with the above-mentioned single apparatus is established (i.e., the plug having a function of input or output in the other apparatus) through a single isochronous channel on the serious bus, and has a function of protecting the connection established once, in the above-mentioned Broadcast connection. Accordingly, the p2p connection is used in case where it is necessary to protect a one-to-one connection between apparatuses for dubbing of music information.
In the above-mentioned Broadcast connection, the transmitting apparatus and the receiving apparatus are subjected independently to a setting operation, without any mutual independence in operation between these apparatuses. In addition, the other apparatus than the apparatus, which has the connection established, or is provided with a control program, which has currently been executed to control the data transmission is permitted to rewrite the plug register of the apparatus, which has the connection established or make a control of the data transmission.
As a result, in the Broadcast connection, it is possible not only to disconnect the connection established between a certain apparatus and the other apparatus, through any other irrelevant apparatus than these apparatuses, but also to compel the isochronous channel for broadcasting, which is utilized in the apparatus connected through the Broadcast connection, to carry out the data transmission, to be switched to the isochronous channel utilized in the above-mentioned other irrelevant apparatus.
On the contrary, with respect to the p2p connection, there exists a convention that only the apparatus, which established the connection or is provided with the above-mentioned control program, can update the plug register corresponding to the plug currently connected to change the connection state (hereinafter referred to as the “operation rule”), in order to achieve the above-mentioned protection of the connection. Such an operation rule is based on the above-mentioned IEC-61883 Part 1 standard.
The protection of the connection for the p2p connection is guaranteed only in the range of the above-mentioned operation rule. On the other hand, there is a possibility that the data transmission is carried out based on the IEEE1394 standard, even between the apparatuses, which are not based on the IEC-61883 Part 1 standard, as mentioned above. Accordingly, it is technically possible for the apparatus, which is not based on the above-mentioned operation rule, but is based on the IEEE 1394 standard, to compel the plug register through which the data transmission is carried out based on the above-mentioned operation rule, to be updated.
As a result, there exists a problem that, in case where the p2p connection is established through the above-mentioned serial bus, the apparatus, which is not based on the IEC-61883 Part 1 standard and is out of the p2p connection standard, may update the plug register of the currently connected plug of the other apparatus, which is connected through the p2p connection, resulting in an unintentional halt of the isochronous transmission in the p2p connection to be prevented.
In addition, even in the apparatus in which the p2p connection is established based on the IEC-61883 Part 1 standard, there is also conceivable a case in which any transmission error occurs for some reasons in the connection. In such a case, the plug register of the apparatus erroneously connected may be updated, thus causing another problem.